Hi, Can any one explain the Renormaliztion Group Method in a simpler way than a pure mathimatics? Is it the link between the molecular space and the macro space? What is the difference between the RNG and LES?

RNG is a mathematical tool to derive turbulence models. LES is one type of simulation where the larger turbulent scales are resolved (ie 3D unsteady) and the smaller scales are modeled with a sub-grid model. There are LES simulations where people use RNG based sub-grid models. There are also RNG models, for example RNG k-epsilon models, where the RNG model is used for all turbulent scales.

The foundations of RNG are not easy to understand - very mathematical stuff. The big "success" of RNG was when it was shown to reproduce almost exactly the k-epsilon form of equations.

One nice book that contains a few chapters on RNG etc. is McComb, "The Physics of Fluid Turbulence". Also look for papers by Yakhot and Orzag.